diff --git a/Changelog.md b/Changelog.md
index 975a1b2b..7903b0f7 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -11,6 +11,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Added end-to-end tests for command-line interface.
   #199 by @MaxDesiatov and @mattt.
+- Added `--minimum-access-level` option to `generate` and `coverage` commands.
+  #219 by @Lukas-Stuehrk.
 
 ### Fixed
 
diff --git a/README.md b/README.md
index c4fc08cc..3cff9d4a 100644
--- a/README.md
+++ b/README.md
@@ -102,6 +102,9 @@ $ apt-get install -y libxml2-dev graphviz
       -f, --format <format>   The output format (default: commonmark)
       --base-url <base-url>   The base URL used for all relative URLs in generated
                               documents. (default: /)
+      --minimum-access-level <minimum-access-level>
+                              The minimum access level of the symbols which should
+                              be included. (default: public)
       -h, --help              Show help information.
 
 The `generate` subcommand 
@@ -131,6 +134,12 @@ $ Documentation/
 └── index.html
 ```
 
+By default,
+`swift-doc` includes only symbols declared as `public` or `open`
+in the generated documentation.
+To include `internal` or `private` declarations,
+pass the `--minimum-access-level` flag with the specified access level.
+
 #### swift-doc coverage
 
     OVERVIEW: Generates documentation coverage statistics for Swift files
@@ -142,6 +151,9 @@ $ Documentation/
 
     OPTIONS:
       -o, --output <output>   The path for generated report 
+      --minimum-access-level <minimum-access-level>
+                              The minimum access level of the symbols which should
+                              be included. (default: public)
       -h, --help              Show help information.
 
 The `coverage` subcommand
@@ -190,6 +202,9 @@ please reach out by [opening an Issue][open an issue]!
       <inputs>                One or more paths to Swift files 
 
     OPTIONS:
+      --minimum-access-level <minimum-access-level>
+                              The minimum access level of the symbols which should
+                              be included. (default: public)
       -h, --help              Show help information.
 
 The `diagram` subcommand
diff --git a/Sources/SwiftDoc/Interface.swift b/Sources/SwiftDoc/Interface.swift
index d5adac70..65e37993 100644
--- a/Sources/SwiftDoc/Interface.swift
+++ b/Sources/SwiftDoc/Interface.swift
@@ -8,14 +8,13 @@ public final class Interface {
 
     public required init(imports: [Import], symbols: [Symbol]) {
         self.imports = imports
-        self.symbols = symbols.filter { $0.isPublic }
+        self.symbols = symbols
 
         self.symbolsGroupedByIdentifier = Dictionary(grouping: symbols, by: { $0.id })
         self.symbolsGroupedByQualifiedName = Dictionary(grouping: symbols, by: { $0.id.description })
         self.topLevelSymbols = symbols.filter { $0.api is Type || $0.id.pathComponents.isEmpty }
 
         self.relationships = {
-            let symbols = symbols.filter { $0.isPublic }
             let extensionsByExtendedType: [String: [Extension]] = Dictionary(grouping: symbols.flatMap { $0.context.compactMap { $0 as? Extension } }, by: { $0.extendedType })
 
             var relationships: Set<Relationship> = []
diff --git a/Sources/SwiftDoc/Symbol.swift b/Sources/SwiftDoc/Symbol.swift
index 1174b6a2..fe2fa345 100644
--- a/Sources/SwiftDoc/Symbol.swift
+++ b/Sources/SwiftDoc/Symbol.swift
@@ -66,6 +66,44 @@ public final class Symbol {
         return false
     }
 
+    public var isPrivate: Bool {
+        // We always assume that `Unknown` is public.
+        guard api is Unknown == false else {
+            return false
+        }
+
+        if api.modifiers.contains(where: { $0.detail == nil && ($0.name == "private" || $0.name == "fileprivate") }) {
+            return true
+        }
+
+        if let `extension` = `extension`,
+           `extension`.modifiers.contains(where: { $0.name == "private" || $0.name == "fileprivate" }) {
+
+            return api.modifiers.allSatisfy { modifier in
+                modifier.detail != nil || (modifier.name != "internal" && modifier.name != "public" && modifier.name != "open")
+            }
+        }
+
+        if let symbol = context.compactMap({ $0 as? Symbol }).last,
+           symbol.api.modifiers.contains(where: { $0.name == "private" || $0.name == "fileprivate" })
+        {
+            switch symbol.api {
+            case is Enumeration:
+                return api is Enumeration.Case
+            case is Protocol:
+                return api is Function || api is Variable
+            default:
+                break
+            }
+        }
+
+        return false
+    }
+
+    public var isInternal: Bool {
+        !isPublic && !isPrivate
+    }
+
     public var isDocumented: Bool {
         return documentation?.isEmpty == false
     }
diff --git a/Sources/swift-doc/Extensions/DCOV+Extensions.swift b/Sources/swift-doc/Extensions/DCOV+Extensions.swift
index fbd423cd..20d375f4 100644
--- a/Sources/swift-doc/Extensions/DCOV+Extensions.swift
+++ b/Sources/swift-doc/Extensions/DCOV+Extensions.swift
@@ -18,10 +18,10 @@ extension Entry {
 // MARK: -
 
 extension Report {
-    public init(module: Module) {
+    public init(module: Module, symbolFilter: (Symbol) -> Bool) {
         let entries = module.sourceFiles
                             .flatMap { $0.symbols }
-                            .filter { $0.isPublic }
+                            .filter(symbolFilter)
                             .map { Entry($0) }
 
         self.init(entries: entries)
diff --git a/Sources/swift-doc/Subcommands/Coverage.swift b/Sources/swift-doc/Subcommands/Coverage.swift
index b26d5a40..63a845ae 100644
--- a/Sources/swift-doc/Subcommands/Coverage.swift
+++ b/Sources/swift-doc/Subcommands/Coverage.swift
@@ -12,6 +12,10 @@ extension SwiftDoc {
             @Option(name: .shortAndLong,
                     help: "The path for generated report")
             var output: String?
+
+            @Option(name: .long,
+                    help: "The minimum access level of the symbols considered for coverage statistics.")
+            var minimumAccessLevel: AccessLevel = .public
         }
 
         static var configuration = CommandConfiguration(abstract: "Generates documentation coverage statistics for Swift files")
@@ -21,7 +25,7 @@ extension SwiftDoc {
 
         func run() throws {
             let module = try Module(paths: options.inputs)
-            let report = Report(module: module)
+            let report = Report(module: module, symbolFilter: options.minimumAccessLevel.includes(symbol:))
 
             if let output = options.output {
                 let encoder = JSONEncoder()
diff --git a/Sources/swift-doc/Subcommands/Diagram.swift b/Sources/swift-doc/Subcommands/Diagram.swift
index 4986df23..280bc596 100644
--- a/Sources/swift-doc/Subcommands/Diagram.swift
+++ b/Sources/swift-doc/Subcommands/Diagram.swift
@@ -11,23 +11,27 @@ extension SwiftDoc {
         struct Options: ParsableArguments {
             @Argument(help: "One or more paths to Swift files")
             var inputs: [String]
+
+            @Option(name: .long,
+                    help: "The minimum access level of the symbols included in the generated diagram.")
+            var minimumAccessLevel: AccessLevel = .public
         }
         
         static var configuration = CommandConfiguration(abstract: "Generates diagram of Swift symbol relationships")
         
         @OptionGroup()
         var options: Options
-        
+
         func run() throws {
             let module = try Module(paths: options.inputs)
-            print(diagram(of: module), to: &standardOutput)
+            print(diagram(of: module, including: options.minimumAccessLevel.includes(symbol:)), to: &standardOutput)
         }
     }
 }
 
 // MARK: -
 
-fileprivate func diagram(of module: Module) -> String {
+fileprivate func diagram(of module: Module, including symbolFilter: (Symbol) -> Bool) -> String {
     var graph = Graph(directed: true)
     
     for (baseClass, subclasses) in module.interface.classHierarchies {
@@ -61,7 +65,7 @@ fileprivate func diagram(of module: Module) -> String {
     }
     
 
-    for symbol in (module.interface.symbols.filter { $0.isPublic && $0.api is Type }) {
+    for symbol in (module.interface.symbols.filter { $0.api is Type }).filter(symbolFilter) {
         let symbolNode = Node("\(symbol.id)")
         graph.append(symbolNode)
 
diff --git a/Sources/swift-doc/Subcommands/Generate.swift b/Sources/swift-doc/Subcommands/Generate.swift
index 616b6658..cca17a59 100644
--- a/Sources/swift-doc/Subcommands/Generate.swift
+++ b/Sources/swift-doc/Subcommands/Generate.swift
@@ -35,6 +35,10 @@ extension SwiftDoc {
       @Option(name: .customLong("base-url"),
               help: "The base URL used for all relative URLs in generated documents.")
       var baseURL: String = "/"
+
+      @Option(name: .long,
+              help: "The minimum access level of the symbols included in generated documentation.")
+      var minimumAccessLevel: AccessLevel = .public
     }
 
     static var configuration = CommandConfiguration(abstract: "Generates Swift documentation")
@@ -55,10 +59,11 @@ extension SwiftDoc {
         var pages: [String: Page] = [:]
 
         var globals: [String: [Symbol]] = [:]
-        for symbol in module.interface.topLevelSymbols.filter({ $0.isPublic }) {
+        let symbolFilter = options.minimumAccessLevel.includes(symbol:)
+        for symbol in module.interface.topLevelSymbols.filter(symbolFilter) {
           switch symbol.api {
           case is Class, is Enumeration, is Structure, is Protocol:
-            pages[route(for: symbol)] = TypePage(module: module, symbol: symbol, baseURL: baseURL)
+            pages[route(for: symbol)] = TypePage(module: module, symbol: symbol, baseURL: baseURL, includingChildren: symbolFilter)
           case let `typealias` as Typealias:
             pages[route(for: `typealias`.name)] = TypealiasPage(module: module, symbol: symbol, baseURL: baseURL)
           case let function as Function where !function.isOperator:
@@ -76,6 +81,9 @@ extension SwiftDoc {
 
         guard !pages.isEmpty else {
             logger.warning("No public API symbols were found at the specified path. No output was written.")
+            if options.minimumAccessLevel == .public {
+              logger.warning("By default, swift-doc only includes public declarations. Maybe you want to use --minimum-access-level to include non-public declarations?")
+            }
             return
         }
 
@@ -93,11 +101,11 @@ extension SwiftDoc {
         } else {
           switch format {
           case .commonmark:
-            pages["Home"] = HomePage(module: module, baseURL: baseURL)
-            pages["_Sidebar"] = SidebarPage(module: module, baseURL: baseURL)
+            pages["Home"] = HomePage(module: module, baseURL: baseURL, symbolFilter: symbolFilter)
+            pages["_Sidebar"] = SidebarPage(module: module, baseURL: baseURL, symbolFilter: symbolFilter)
             pages["_Footer"] = FooterPage(baseURL: baseURL)
           case .html:
-            pages["Home"] = HomePage(module: module, baseURL: baseURL)
+            pages["Home"] = HomePage(module: module, baseURL: baseURL, symbolFilter: symbolFilter)
           }
 
           try pages.map { $0 }.parallelForEach {
diff --git a/Sources/swift-doc/Supporting Types/AccessLevel.swift b/Sources/swift-doc/Supporting Types/AccessLevel.swift
new file mode 100644
index 00000000..30de853f
--- /dev/null
+++ b/Sources/swift-doc/Supporting Types/AccessLevel.swift	
@@ -0,0 +1,16 @@
+import ArgumentParser
+import SwiftDoc
+
+enum AccessLevel: String, ExpressibleByArgument {
+    case `public`
+    case `internal`
+
+    func includes(symbol: Symbol) -> Bool {
+        switch self {
+        case .public:
+            return symbol.isPublic
+        case .internal:
+            return symbol.isPublic || symbol.isInternal
+        }
+    }
+}
diff --git a/Sources/swift-doc/Supporting Types/Components/Members.swift b/Sources/swift-doc/Supporting Types/Components/Members.swift
index d7d26a32..b653b25d 100644
--- a/Sources/swift-doc/Supporting Types/Components/Members.swift	
+++ b/Sources/swift-doc/Supporting Types/Components/Members.swift	
@@ -18,14 +18,14 @@ struct Members: Component {
     var methods: [Symbol]
     var genericallyConstrainedMembers: [[GenericRequirement] : [Symbol]]
 
-    init(of symbol: Symbol, in module: Module, baseURL: String) {
+    init(of symbol: Symbol, in module: Module, baseURL: String, symbolFilter: (Symbol) -> Bool) {
         self.symbol = symbol
         self.module = module
         self.baseURL = baseURL
 
         self.members = module.interface.members(of: symbol)
             .filter { $0.extension?.genericRequirements.isEmpty != false }
-            .filter { $0.isPublic }
+            .filter(symbolFilter)
 
         self.typealiases = members.filter { $0.api is Typealias }
         self.initializers = members.filter { $0.api is Initializer }
diff --git a/Sources/swift-doc/Supporting Types/Pages/HomePage.swift b/Sources/swift-doc/Supporting Types/Pages/HomePage.swift
index 425c8d89..27090a08 100644
--- a/Sources/swift-doc/Supporting Types/Pages/HomePage.swift	
+++ b/Sources/swift-doc/Supporting Types/Pages/HomePage.swift	
@@ -16,11 +16,11 @@ struct HomePage: Page {
     var globalFunctions: [Symbol] = []
     var globalVariables: [Symbol] = []
 
-    init(module: Module, baseURL: String) {
+    init(module: Module, baseURL: String, symbolFilter: (Symbol) -> Bool) {
         self.module = module
         self.baseURL = baseURL
 
-        for symbol in module.interface.topLevelSymbols.filter({ $0.isPublic }) {
+        for symbol in module.interface.topLevelSymbols.filter(symbolFilter) {
             switch symbol.api {
             case is Class:
                 classes.append(symbol)
diff --git a/Sources/swift-doc/Supporting Types/Pages/SidebarPage.swift b/Sources/swift-doc/Supporting Types/Pages/SidebarPage.swift
index 7b71908b..cbbce3b0 100644
--- a/Sources/swift-doc/Supporting Types/Pages/SidebarPage.swift	
+++ b/Sources/swift-doc/Supporting Types/Pages/SidebarPage.swift	
@@ -14,11 +14,11 @@ struct SidebarPage: Page {
     var globalFunctionNames: Set<String> = []
     var globalVariableNames: Set<String> = []
 
-    init(module: Module, baseURL: String) {
+    init(module: Module, baseURL: String, symbolFilter: (Symbol) -> Bool) {
         self.module = module
         self.baseURL = baseURL
 
-        for symbol in module.interface.topLevelSymbols.filter({ $0.isPublic }) {
+        for symbol in module.interface.topLevelSymbols.filter(symbolFilter) {
             switch symbol.api {
             case is Class:
                 typeNames.insert(symbol.id.description)
diff --git a/Sources/swift-doc/Supporting Types/Pages/TypePage.swift b/Sources/swift-doc/Supporting Types/Pages/TypePage.swift
index 244e736a..b3bee3f7 100644
--- a/Sources/swift-doc/Supporting Types/Pages/TypePage.swift	
+++ b/Sources/swift-doc/Supporting Types/Pages/TypePage.swift	
@@ -7,12 +7,14 @@ struct TypePage: Page {
     let module: Module
     let symbol: Symbol
     let baseURL: String
+    let symbolFilter: (Symbol) -> Bool
 
-    init(module: Module, symbol: Symbol, baseURL: String) {
+    init(module: Module, symbol: Symbol, baseURL: String, includingChildren symbolFilter: @escaping (Symbol) -> Bool) {
         precondition(symbol.api is Type)
         self.module = module
         self.symbol = symbol
         self.baseURL = baseURL
+        self.symbolFilter = symbolFilter
     }
 
     // MARK: - Page
@@ -27,7 +29,7 @@ struct TypePage: Page {
 
             Documentation(for: symbol, in: module, baseURL: baseURL)
             Relationships(of: symbol, in: module, baseURL: baseURL)
-            Members(of: symbol, in: module, baseURL: baseURL)
+            Members(of: symbol, in: module, baseURL: baseURL, symbolFilter: symbolFilter)
             Requirements(of: symbol, in: module, baseURL: baseURL)
         }
     }
@@ -41,7 +43,7 @@ struct TypePage: Page {
 
         \#(Documentation(for: symbol, in: module, baseURL: baseURL).html)
         \#(Relationships(of: symbol, in: module, baseURL: baseURL).html)
-        \#(Members(of: symbol, in: module, baseURL: baseURL).html)
+        \#(Members(of: symbol, in: module, baseURL: baseURL, symbolFilter: symbolFilter).html)
         \#(Requirements(of: symbol, in: module, baseURL: baseURL).html)
         """#
     }
diff --git a/Tests/SwiftDocTests/InterfaceTypeTests.swift b/Tests/SwiftDocTests/InterfaceTypeTests.swift
index 0c3db153..42ba0ba9 100644
--- a/Tests/SwiftDocTests/InterfaceTypeTests.swift
+++ b/Tests/SwiftDocTests/InterfaceTypeTests.swift
@@ -31,12 +31,11 @@ final class InterfaceTypeTests: XCTestCase {
         // `class C`
         let classC = sourceFile.symbols[2]
         XCTAssert(classC.api is Class)
-        
-        // Class B does not exist in subclasses because it's not public
-        // Class C exists in subclasses because it's public
+
         let subclasses = module.interface.typesInheriting(from: classA)
-        XCTAssertEqual(subclasses.count, 1)
-        XCTAssertEqual(subclasses[0].id, classC.id)
+        XCTAssertEqual(subclasses.count, 2)
+        XCTAssertEqual(subclasses[0].id, classB.id)
+        XCTAssertEqual(subclasses[1].id, classC.id)
     }
 
     func testInternalMembers() throws {
@@ -60,7 +59,7 @@ final class InterfaceTypeTests: XCTestCase {
         let module = Module(name: "Module", sourceFiles: [sourceFile])
 
         XCTAssertEqual(sourceFile.symbols.count, 5)
-        XCTAssertEqual(module.interface.symbols.count, 1)
+        XCTAssertEqual(module.interface.symbols.count, 5)
 
         // `struct A`
         do {
@@ -87,12 +86,22 @@ final class InterfaceTypeTests: XCTestCase {
 
         XCTAssertEqual(sourceFile.symbols.count, 5)
         XCTAssertTrue(sourceFile.symbols[0].isPublic, "Function `a()` should BE marked as public - its visibility is specified by extension")
+        XCTAssertFalse(sourceFile.symbols[0].isInternal, "Function `a()` should NOT be marked as internal")
+        XCTAssertFalse(sourceFile.symbols[0].isPrivate, "Function `a()` should NOT be marked as private")
         XCTAssertTrue(sourceFile.symbols[1].isPublic, "Function `b()` should BE marked as public - its visibility is public")
+        XCTAssertFalse(sourceFile.symbols[1].isInternal, "Function `b()` should NOT be marked as internal")
+        XCTAssertFalse(sourceFile.symbols[1].isPrivate, "Function `b()` should NOT be marked as private")
         XCTAssertFalse(sourceFile.symbols[2].isPublic, "Function `c()` should NOT be marked as public - its visibility is internal")
+        XCTAssertTrue(sourceFile.symbols[2].isInternal, "Function `c()` should BE marked as internal - its visibility is internal.")
+        XCTAssertFalse(sourceFile.symbols[2].isPrivate, "Function `c()` should NOT be marked as private")
         XCTAssertFalse(sourceFile.symbols[3].isPublic, "Function `d()` should NOT be marked as public - its visibility is fileprivate")
+        XCTAssertFalse(sourceFile.symbols[3].isInternal, "Function `d()` should NOT be marked as internal - its visibility is fileprivate")
+        XCTAssertTrue(sourceFile.symbols[3].isPrivate, "Function `d()` should BE marked as public - its visibility is fileprivate")
         XCTAssertFalse(sourceFile.symbols[4].isPublic, "Function `e()` should NOT be marked as public - its visibility is private")
+        XCTAssertFalse(sourceFile.symbols[4].isInternal, "Function `e()` should NOT be marked as public - its visibility is private")
+        XCTAssertTrue(sourceFile.symbols[4].isPrivate, "Function `e()` should BE marked as private - its visibility is private")
 
-        XCTAssertEqual(module.interface.symbols.count, 2)
+        XCTAssertEqual(module.interface.symbols.count, 5)
         XCTAssertEqual(module.interface.symbols[0].name, "a()", "Function `a()` should be in documented interface")
         XCTAssertEqual(module.interface.symbols[1].name, "b()", "Function `b()` should be in documented interface")
     }
@@ -114,14 +123,27 @@ final class InterfaceTypeTests: XCTestCase {
 
         XCTAssertEqual(sourceFile.symbols.count, 5)
         XCTAssertTrue(sourceFile.symbols[0].isPublic, "Property `a` should BE marked as public - its visibility is specified by extension")
+        XCTAssertFalse(sourceFile.symbols[0].isInternal, "Property `a` should NOT be marked as internal - its visibility is specified public by extension")
+        XCTAssertFalse(sourceFile.symbols[0].isPrivate, "Property `a` should NOT be marked as private - its visibility is specified public by extension")
         XCTAssertTrue(sourceFile.symbols[1].isPublic, "Property `b` should BE marked as public - its visibility is public")
+        XCTAssertFalse(sourceFile.symbols[1].isInternal, "Property `b` should NOT be marked as internal - its visibility is public")
+        XCTAssertFalse(sourceFile.symbols[1].isPrivate, "Property `b` should NOT be marked as private - its visibility is public")
         XCTAssertFalse(sourceFile.symbols[2].isPublic, "Property `c` should NOT be marked as public - its visibility is internal")
+        XCTAssertTrue(sourceFile.symbols[2].isInternal, "Property `c` should BE marked as internal - its visibility is internal")
+        XCTAssertFalse(sourceFile.symbols[2].isPrivate, "Property `c` should NOT be marked as private - its visibility is internal")
         XCTAssertFalse(sourceFile.symbols[3].isPublic, "Property `d` should NOT be marked as public - its visibility is fileprivate")
+        XCTAssertFalse(sourceFile.symbols[3].isInternal, "Property `d` should NOT be marked as internal - its visibility is fileprivate")
+        XCTAssertTrue(sourceFile.symbols[3].isPrivate, "Property `d` should BE marked as private - its visibility is fileprivate")
         XCTAssertFalse(sourceFile.symbols[4].isPublic, "Property `e` should NOT be marked as public - its visibility is private")
+        XCTAssertFalse(sourceFile.symbols[4].isInternal, "Property `e` should NOT be marked as internal - its visibility is private")
+        XCTAssertTrue(sourceFile.symbols[4].isPrivate, "Property `e` should BE marked as public - its visibility is private")
 
-        XCTAssertEqual(module.interface.symbols.count, 2)
+        XCTAssertEqual(module.interface.symbols.count, 5)
         XCTAssertEqual(module.interface.symbols[0].name, "a", "Property `a` should be in documented interface")
         XCTAssertEqual(module.interface.symbols[1].name, "b", "Property `b` should be in documented interface")
+        XCTAssertEqual(module.interface.symbols[2].name, "c", "Property `c` should be in documented interface")
+        XCTAssertEqual(module.interface.symbols[3].name, "d", "Property `d` should be in documented interface")
+        XCTAssertEqual(module.interface.symbols[4].name, "e", "Property `e` should be in documented interface")
     }
 
     func testComputedPropertiesWithMultipleAccessModifiersInPublicExtension() throws {
@@ -156,10 +178,20 @@ final class InterfaceTypeTests: XCTestCase {
 
         XCTAssertEqual(sourceFile.symbols.count, 5)
         XCTAssertTrue(sourceFile.symbols[0].isPublic, "Property `a` should be marked as public - the visibility of its getter is public")
+        XCTAssertFalse(sourceFile.symbols[0].isInternal, "Property `a` should not be marked as internal - the visibility of its getter is public")
+        XCTAssertFalse(sourceFile.symbols[0].isPrivate, "Property `a` should not be marked as private - the visibility of its getter is public")
         XCTAssertTrue(sourceFile.symbols[1].isPublic, "Property `b` should be marked as public - the visibility of its getter is public")
+        XCTAssertFalse(sourceFile.symbols[1].isInternal, "Property `b` should not be marked as internal - the visibility of its getter is public")
+        XCTAssertFalse(sourceFile.symbols[1].isPrivate, "Property `b` should not be marked as private - the visibility of its getter is public")
         XCTAssertTrue(sourceFile.symbols[2].isPublic, "Property `c` should be marked as public - the visibility of its getter is public")
+        XCTAssertFalse(sourceFile.symbols[2].isInternal, "Property `c` should not be marked as internal - the visibility of its getter is public")
+        XCTAssertFalse(sourceFile.symbols[2].isPrivate, "Property `c` should not be marked as private - the visibility of its getter is public")
         XCTAssertTrue(sourceFile.symbols[3].isPublic, "Property `d` should be marked as public - the visibility of its getter is public")
+        XCTAssertFalse(sourceFile.symbols[3].isInternal, "Property `d` should not be marked as internal - the visibility of its getter is public")
+        XCTAssertFalse(sourceFile.symbols[3].isPrivate, "Property `d` should not be marked as private - the visibility of its getter is public")
         XCTAssertTrue(sourceFile.symbols[4].isPublic, "Property `e` should be marked as public - the visibility of its getter is public")
+        XCTAssertFalse(sourceFile.symbols[4].isInternal, "Property `e` should not be marked as internal - the visibility of its getter is public")
+        XCTAssertFalse(sourceFile.symbols[4].isPrivate, "Property `e` should not be marked as private - the visibility of its getter is public")
 
         XCTAssertEqual(module.interface.symbols.count, 5)
         XCTAssertEqual(module.interface.symbols[0].name, "a", "Property `a` should be in documented interface")
@@ -198,11 +230,14 @@ final class InterfaceTypeTests: XCTestCase {
         let sourceFile = try SourceFile(file: url, relativeTo: url.deletingLastPathComponent())
         let module = Module(name: "Module", sourceFiles: [sourceFile])
 
-        XCTAssertEqual(module.interface.symbols.count, 5)
+        XCTAssertEqual(module.interface.symbols.count, 8)
         XCTAssertEqual(module.interface.symbols[0].name, "RootController")
         XCTAssertEqual(module.interface.symbols[1].name, "ControllerExtension")
         XCTAssertEqual(module.interface.symbols[2].name, "public_properties")
-        XCTAssertEqual(module.interface.symbols[3].name, "ExtendedProperties")
-        XCTAssertEqual(module.interface.symbols[4].name, "public_prop")
+        XCTAssertEqual(module.interface.symbols[3].name, "internal_properties")
+        XCTAssertEqual(module.interface.symbols[4].name, "ExtendedProperties")
+        XCTAssertEqual(module.interface.symbols[5].name, "public_prop")
+        XCTAssertEqual(module.interface.symbols[6].name, "InternalProperties")
+        XCTAssertEqual(module.interface.symbols[7].name, "internal_prop")
     }
 }
diff --git a/action.yml b/action.yml
index 46c691e6..9f26e8be 100644
--- a/action.yml
+++ b/action.yml
@@ -20,6 +20,10 @@ inputs:
     description: "The path for generated output"
     required: true
     default: "./.build/documentation"
+  minimum-access-level:
+    description: "The minimum access level of the symbols which should be included (public, internal, or private)"
+    required: false
+    default: "public"
 
 runs:
   using: "docker"
@@ -36,6 +40,8 @@ runs:
       "${{ inputs.module-name }}",
       --output,
       "${{ inputs.output }}",
+      --minimum-access-level,
+      "${{ inputs.minimum-access-level }}"
     ]
 
 branding: